Hydrostatic transmissions have two or more hydrostatic units utilizing rotating cylinder blocks of similar construction that are hydraulically connected. One cylinder block, normally referred to as the pump, is connected to a rotatable input shaft, and the other cylinder block, referred to as a motor, has a power output shaft. These cylinder blocks or groups typically are of the piston/swashplate design or are of a bent-axis design. Each of these designs have certain beneficial design features, but both also have certain structural and functional shortcomings. This invention combines the best of these two designs, and substantially eliminates the shortcomings of each. Further advantages are realized by this invention that are not present in either of the prior designs.
Specifically, the ball and socket joint at the piston/slipper interface was characteristic of both bent-axis and swashplate designs. An extended arm that reaches toward and sometimes inside the piston bore was characteristic of only the bent-axis design. A hydrostatic bearing-surface that slides between the slipper and the swashplate was characteristic of the swashplate design.
The prior swashplate designs had substantial side-load on the pistons creating greater friction between the pistons and bores, which adversely affected torque efficiency. Only low swashplate angles were available which limited power output. The load carrying point of the shaft (i.e., the "sweet spot") was located by the length of the cylinder in a position which invited failure at the interface between the cylinder block and the shaft. The greater length of existing blocks required a longer shaft which invited shaft deflection which reduced the life of shaft bearings.
Therefore, a principal object of this invention is to provide a rotating cylinder for a swashplate-type hydrostatic transmission that will create a substantial reduction in piston surface pressure between the pistons of the cylinder and the piston bores, and to thereby improve the torque efficiency of the machine being driven by the transmission.
A further object of this invention is to provide a rotating cylinder for a swashplate-type hydrostatic transmission wherein higher swashplate angles are achievable to improve power output and overall efficiency of the machine.
A still further object of this invention is to provide a rotating cylinder for swashplate-type hydrostatic transmissions which moves the load-carrying point of the shaft closer to the valve plate end of the cylinder block to increase the strength of the interface between the cylinder block and the shaft to prevent failure of the interface.
A still further object of this invention is to provide a rotating cylinder block for swashplate-type hydrostatic transmissions which will have a sweet spot closer to the valve plate end of the cylinder block, and which will reduce the overhang length of the piston, which allows for a reduction in the overall length of the machine package.
A still further object of this invention is to provide a rotating cylinder for a swashplate-type hydrostatic transmission which will permit a reduction in the length of the shaft which in turn will increase the bearing life for the shaft bearings.
These and other objects will be apparent to those skilled in the art.